Monthly Archives: March 2016

Chapter 2

As I explained in Chapter 1, while being very pleased with the sound of my newly constructed eTap2hw echo box I really wanted a way to store some settings for the tunes I played regularly.

My previous echo machine had been a Zoom RFX2000 with the EFTP programs from Charlie Hall. These programs or patches were numbered from 0-42 on the Zoom’s two digit seven-segment display and they came with a list of suggested patches for the common tunes by The Shadows.

The Zoom RFX2000 displays two-digit preset numbers

Having been able to compare the sound of the RFX2000, which I had been previously pretty happy with, to the warmer and more ‘analog’ sounding eTap2hw, I decided to try to add the ability to store the settings for the tunes to the eTap2hw so I could recall them easily. The Zoom RFX2000 still required you to either remember or look up the patch number in a printed list of tunes.

My original short ‘wish list’ was something along the lines of:

Ability to name patches, for example “Apache” or “Wonderful Land”.

Be able to adjust the effect parameters by using real knobs,

and store and recall these settings easily.

To which I added, as possible future additions:

Interface via USB with a computer for backing up and restoring patches

Addition of MIDI control to select patches, possibly by using a MIDI foot controller or by sending program change messages from a sequencer playing the backing track.

About this time I discovered some forum postings by a guy in the USA called Johan Forrer who had come up with a design for the automation circuit and had produced a simple version of the software to drive it, for the Arduino platform. When I got in touch with Johan he very kindly and with no hesitation, sent me the source code for his automation.

One of Johan Forrer’s early prototypes with basic automation from October 2012.

Having studied his code I quickly realised it wouldn’t fulfil my basic requirement of being able to name the patches to match the tunes: he had allowed for 8 presets (basically one for each of the 8 emulations in Piet’s SKRM-eTap2hw module) and only four user patches which could not be named, only referred to by number. Each could use any of the 8 emulation presets and you could set the values of the three parameters of each by hitting the up and down buttons but there was no provision for setting the parameters with real knobs.

Johan’s code did, however, have the basic structure that would be needed so, with his permission, I started to ‘hack’ it and add the features I’d planned. First though I needed the hardware on which to run the automation and, whilst Johan had built his own Atmel Arduino-like microcontroller circuit I decided to go for an off the shelf Arduino Uno and an LCD/Buttons shield kit from Adafruit.

The latter would be more or less essential to leave enough free inputs and outputs on the Arduino to satisfy my ambitious plans. As it connects to the Arduino via the I2C bus, it required only two input/output lines to operate both the LCD and the buttons, rather than the more normal parallel LCD drive which needs up to seven of the Arduino’s precious digital pins.

In the manual eTap2hw design the three parameter pots are connected directly to the SKRM module’s P0, P1 and P2 inputs. These each provide a variable DC voltage between 0 and 3.3V that is read by the DSP code running on the FV-1 chip on the module and can used to alter the parameters, depending on what the code has been designed to do. Piet’s eTap2hw code mainly used P0 to control the mix of wet and dry signal, P1 was a program or ‘heads’ control which usually emulated the heads switch on the Meazzi and Vox echo machines and P2 was usually controlling the feedback or ‘repeats’ of the echoes.

To automate the system these pots had to be disconnected from the echo module and instead the voltages they were outputting would be read by three analog inputs on the Arduino. As the Arduino operates at 5V logic levels and the FV-1 operates at 3.3V logic levels, the pots would have to be wired to GND and +5V rather than +3.3V and some sort of interface would be needed to drop the Arduino’s ‘analog’ outputs to a 0 – 3.3V range.

The P0, P1 and P2 inputs on the echo module would now be driven by dc voltages output from the Arduino. A complication was that the Arduino’s analog outputs are not true analog DC voltages. Instead they use a system of pulse width modulation (PWM) to generate the output and not a true DC voltage – the wider the pulse the higher the average voltage:

Johan and Piet together had already solved these two problems by coming up with a low-pass filter combined with a voltage divider that would both smooth the PWM to give true DC and at the same time reduce it from 5V max to 3.3V max. You can see one of these on the left hand end of the breadboard in the following photo of my first test-bed prototype.

My first bread-boarded automation test-bed. January 2013

The blue trimmer pot on the right is connected to an analog input pin on the Arduino and the LCD is showing which button was last pressed and the analog input value being read from the pot wiper. The buttons board assembly which I built on Veroboard actually ended up being used in my first completed Echotapper Vintage Echo Unit – until the buttons wore out!

At this point Piet came up with a great little design for a shield that would do all the interfacing between the Arduino, the pots and the SKRM-eTap2hw echo module.He called it the Universal I/O Shield and it certainly simplified the wiring required as it would stack on top of the Arduino and the LCD shield would stack on top of that. The only wiring required would be to the external pots, the eTap2hw motherboard and the 12V dc power supply.

The Universal I/O shield takes care of all the PWM filtering and logic level shifting between the Arduino and the echo module.

The Universal I/O Shield stacked on top of the Arduino Uno.

Having proved my ideas were going to be feasible I continued to develop the software for the automation, which I’ll refer to as firmware from now on to avoid any confusion with any software possibly running on the PC.

In parallel with the firmware development I looked for a suitable enclosure that could house the project and after much deliberation, measurement and ‘guesstimating’ I settled on a Hammond 1455N2201 Extruded Aluminium Enclosure measuring 223 x 103 x 53mm. As you’ll see below, it was quite a squeeze to fit it all in!

End view of the LCD + I/O + Arduino stack.

SKRM-ETAP2 module and Piet’s preamp/motherboard on the left with the Arduino + Universal I/O + LCD Shield on the right. MIDI In and Out sockets also got included!

The finished unit turned out very well and I even managed to include the MIDI control that had been on the ‘nice but maybe later’ wish-list.

The Automation Version Completed – January 2013

Word had begun to get around and this project seemed to be generating a good bit of interest from The Shadows forums. Steve Mitchell, who would come to play an important role in the Blue Nebula Team, was probably the first builder to take on the task of emulating my efforts. As he says himself

I eventually got into the Automated eTap2HW after managing to contact Piet who kindly pointed me in the direction of Newtone. Then I realised that there was also an Arduino based automation, which Piet was supporting with his interface shield PCB. So I contacted Johan, Lars and yourself and it went from there when I decided to “bite the bullet” and go for broke without ever building a manual version. Once I’d purchased the interface from Piet then off I went now firmly attached to your “Journey”.

Though doing a few things a little differently, such as using a larger enclosure (good decision Steve!), by April 2013 Steve had become the proud owner of another eTap2HW plus automation or, as he called it on his excellent front panel, his “EchoTapper Vintage Echoes of the Sixties.”

The Finished Project by Steve Mitchell

While working with Steve and helping him with his project we formed a close working relationship and soon Steve was coming up with some great suggestions for improving the firmware and some clever ideas to get an even better sound out of Piet’s analog preamp design – but that will have to wait for Chapter 3!

Like this:

“Go back?” he thought. “No good at all! Go sideways? Impossible! Go forward? Only thing to do! On we go!”
― J.R.R. Tolkien, The Hobbit

Chapter One

Back in February 2013 (is it really over three years ago?) I started this blog with the idea of documenting a little project that I had been working on since the previous November.

Little did I know, like Bilbo Baggins in “The Hobbit”, where my ‘unexpected journey’ would lead. In the next few posts I’m going to recount how this …

November 2012: The First Prototype. It won’t win any prizes for good looks!

ended up with this …

March 2016: The Blue Nebula

I’d been using a Zoom RFX2000 with the EFTP patches for a couple of years but my ears pricked up back in November 2012 when I heard a couple of demos by Dave Robinson of a new (to me) echo circuit called the eTap2hw which had been designed by Piet Verbruggen.

I couldn’t find anywhere to get a kit to try it our for myself so I posted a question on the ShadowMusic forum and discovered that the kit could be bought from Newtone in Piet’s homeland of the Netherlands. Even then I had to email the guys at Newtone to find out the price and order details.

I managed to order a kit and it went together without any problems thanks to the very detailed instructions Piet had provided on his Echotapper blog and it worked first time. I’d had a lot of experience since I was a young ‘un of building and designing electronics so that probably helped so before November 2012 was out I had a working prototype that, while not pretty (I’d built it in a die-cast box from an old project lying in my garage), it sounded just wonderful. Not only were the echo timings apparently spot on for the various vintage echo machines it was emulating but the unit had a nice warm sound that belied the digital signal processing that lay behind those emulations.

Having heard my prototype in action at the Northern Ireland Shadows Club, my good friend and el-president of the Club, Des McNeill, also started raving (nothing unusual there) about how good and ‘analog’ the eTap2hw sounded so we ended up buying another three kits, two for Des to build and another one for me. What had we started here!

It was now time to produce a proper housing for the eTap2hw’s we were building and Des’ skill as an aero modeller came to the fore here. Des and I worked out a design for the front and rear panels which he then had made up by a company in Belfast. By the time of our next Club meeting Des had his new enclosure built and the first kit assembled and ready to try out and it looked and sounded great.

The boxes Des designed and made (remember I said he was an aero modeller) were constructed beautifully from precision cut plywood, lined on the inside with aluminium foil for screening and covered on the outside with a lovely beige tolex.

The manual unit, front view

The Ins and Outs.

These proved so popular with the Club members that Des ended up building five or six more of them and they are still in use regularly on Club days and by the guys who play gigs.

While I was delighted with the sound of my eTap2hw there was one thing I thought it needed to make it even better: a way to store the settings for individual tunes – mainly because I kept forgetting which echo to use for a given tune – TMB syndrome (too many birthdays!).

Thus began the next stage of the journey – automation, as will be revealed in Chapter Two.

Like this:

The release Version 3.0 of the Blue Nebula firmware and the matching Librarian app Version 3.0 are undergoing final testing and will be released here shortly.

A quick glance at the new Librarian User Guide (link below) will show you the many interesting features and how it works with the Blue Nebula to give a really unique and exciting new effect pedal experience.

Briefly, the Librarian app allows you to transfer your patches between the Blue Nebula and your computer and it allows you to back them up by saving onto the computer – but it does a LOT more!

It also allows you to edit your patches, for example renaming them or tweaking the parameters, as well as having copy and paste functions and it allows you to create set lists so you can have the tunes arranged in the order you want for a show. The up and down footswitches then allow you to step through the list with the LCD display showing you the name of each tune.

The Blue Nebula comes with 8 vintage echo effects already installed in its first memory chip (MEM 1) but the new Librarian’s biggest and most unique feature is probably its ability to upload another 8 effects via USB to the second memory chip (MEM 2). This updates the effect and parameter names on both the Blue Nebula pedal and in the Librarian app which will recall them next time it’s run so that it always stays in sync with the effects on-board the pedal.

These additional 8 effects can be chosen from a wide range to standard guitar effects that are already available on the internet – many free DSP programs are listed on the Spin Semiconductors website. In addition there are several unique new effects that the Blue Nebula design team is currently working on and we will be making these available (also free) ready to upload to the Blue Nebula via the USB input.

‘Standard’ effects include popular guitar effects including chorus, phaser, flanger, delays and reverbs and the new effects currently in development include emulations of the classic Binson Echorec and an enhanced Vox Long Tom emulation.

Like this:

As some of you will have heard on social media and various forums a new guitar effects pedal to be called the Blue Nebula will be launching soon. The Blue Nebula is a compact stomp-box style effects pedal design with a strong emphasis on accurately emulating the sounds of vintage tape-based echo units but with the ability for users to upload new effects that cover a wide range of other popular sounds.Designed by a four-man team including yours truly (firmware and software), Steve Mitchell (new analog preamp design), Piet Verbruggen (DSP programming) and Mick Taylor (hardware and PCB design), the Blue Nebula is released as an open source/open hardware project.

The Blue Nebula will be available as a kit or built-to-order. Prices to be confirmed.

Main Features

Accurately emulates many classic tape echo machines

Can be loaded with up to 8 additional general guitar effects such as chorus, phaser, reverbs, shimmer verb and other echo effects which can be uploaded via USB

Other effects in the pipeline include emulations of the classic Binson Echorec (think Pink Floyd) and an enhanced Vox Long Tom echo.

Three parameter control knobs which, for example, can control dry/wet mix, feedback or chorus rate.

Built-in USB and MIDI In ports

All firmware updates and new effect sets are uploaded via a normal USB cable – no need for additional special ‘programmers’.

Some links to the Blue Nebula User Manual, the Building Instructions and the Bill of Materials are given below.

If you are thinking of building a Blue Nebula please read the Building Instructions thoroughly to determine if it is within your capabilities. Most of the components are through-hole types but there are a few surface mount components. The kit can be supplied with these already soldered in place for you.